Commonization is the story of similarities and differences, of patterns among multiple systems. In a collection of systems, what is common to all and what varies? And which of the commonalities and variabilities do we want to model? By focusing on models of collections of systems rather than individual systems, we can capture patterns in a given domain or discipline, and those patterns represent knowledge. Commonization is the model space dimension that enables knowledge to be accumulated in the model space, shared, and used in the application of SE. e region of a model is important in this dimension.